1. Field of the invention
The present invention relates to a process and a device for supplying and transporting flat and curved substrates of whatever shape (made of material such as glass or plastic) into industrial vacuum systems for application of surface coatings on the substrates.
2. Description of the Prior Art
These systems can be designed according to two distinct operating concepts that are realized into so-called in-line and oscillating systems respectively, with the substrates positioned horizontally or vertically.
The in-line type systems are characterised by the fact that the various stages of the process take place in a continuous manner as the substrates are transferred through the various coating areas.
In the oscillating type systems, on the other hand, there is a single coating area, and the substrates are moved through this in both directions with an alternating straight movement. The process is stopped at the end of each passage of the substrates through the coating area, in order to set up the system for the next coating operation.
In both cases, feeding of the substrates into the system is carried out using the batch principle. This principle consists of positioning a suitable number of substrates on the loading surface and then introducing them all together into the system. The group of substrates formed in this way is passed through all the subsequent stations in the system in order to undergo the coating process, without modification, until reaching the unloading point.
In order to clarify the description of the present invention, among the many possible applications the one that will be taken into consideration here, without in any way limiting the use of the invention itself, relates to the feeding and transport of substrates of flat/curved/shaped glass through vacuum systems, and in particular that in industrial plants for deposit of transparent and/or non-transparent thin layers using the technology known in the art as magnetotronic sputtering, in all its various constructional embodiments.
In the following description the word coating is used to indicate one or more thin layers applied to the substrate.
The technical solution based on the batch principle is only optimal when processing single sheets of a size equal to that of the working loading area.
In reality it is also necessary to coat sheets of glass of smaller size and with different geometrical shapes (for example triangles, trapeziums, semicircles, etc.). In these cases the average saturation of the loading surface can be lower than the optimum value by a level of around 30 percent or more, which thus causes a loss of production capacity of the same amount.
Setting aside the concept of batch feeding, there are a number of transport systems that are generally used.
For example, in the case of flat substrates a roller and/or belt conveyor is used, while for curved substrates a creeper or carriage conveyor is used.
All the above mentioned conveyor systems in no way make it possible to avoid a lack of saturation in the batch itself.
Of the two type of systems mentioned above, the in-line solution is normally used in plants working flat substrates.
For curved substrates, oscillating systems are preferred, as the creation of an in-line type system for curved substrates based on the batch feeding concept involves the following problems:
excessive length of the line, as a result of the need to separate the process gasses used in the various deposition areas with units of three chambers, two transfer chambers and one isolation chamber, of a working length equivalent to that of the batch PA1 high investment costs for purchase of the system PA1 low saturation of the loading area, with a consequent loss of production capacity PA1 high level of surface pollution in the process chambers by the material being deposited. PA1 reduction in the pollution of the surfaces in the coating chambers with the deposition material, due to the high level of unsaturation of the loading area (this is also the case with a creeper conveyor system) PA1 reduction of the total width of the line (this is also the case with a creeper conveyor system) PA1 lower investments required for creation of the plants (this is also the case with a creeper conveyor system) PA1 elimination of manual operations to load and unload the sheets of glass from the carriages PA1 increased productivity for plant operators PA1 elimination of carriage maintenance costs and those relating to the manpower required to set up the supports on the carriages whenever there are changes in production.
As mentioned above, the batch feeding system causes a decrease in the production capacity when the substrates are of a size lower than the maximum area of the loading surface. This is so regardless of the conveyor system used (both horizontal and vertical conveyors, roller beds, belt conveyors, creepers) and the type of system (in-line or oscillating).
For example, let us consider a sputtering system with a working width of 2000 mm and with a loading area of 2000 mm.times.3000 mm, for coating of glass substrates.
In the case of flat sheets of glass, using a roller conveyor system it is possible, for example, to load up to a maximum of 3 sheets with a height of 960 mm each, taking into account a minimum spacing of 40 mm between sheets. If sheets of a greater height must be processed, for example sheets of 970 mm, it will only be possible to house two sheets per batch, with a loss in saturation of the loading surface of 31.3 percent, which in this way gives a drop in saturation of from 96% to 64.7%, with a corresponding drop in production capacity.
In the case of curved sheets of glass, using a carriage conveyor system, the structure supporting the pieces, which is formed on the carriages themselves, requires a greater distance between sheets, so that saturation of the loading area is further reduced. In this case it would be possible, for example, to house up to a maximum of 3 sheets with a height of 900 mm on the same carriage (=load). If the height of the sheets rises, for example, to 910 mm, it will only be possible to position two sheets per carriage, with a loss in saturation of the loading area of 29.3 percent (from 90% to 60.7%) and an equivalent loss in production capacity.
In the case of curved sheets of glass using a creeper transport system, the saturation levels would be the same as those indicated for flat glass on a roller conveyor.